1: Place the turkey, cilantro, jalapeño(s), scallion, chile powder, and cumin in a mixing bowl and, using a wooden spoon, stir to mix.
2: Divide the turkey into 4 equal portions. Shape each portion into a patty about 1 inch thick (lightly wet your hands with cold water before handling the meat). Work with a light touch, handling the meat as little as possible. Make a slight depression in the center of the patties; they should be slightly concave. You can form the burgers up to 6 hours ahead. Arrange the burgers on a plate lined with plastic wrap and cover them with more plastic wrap. Refrigerate the burgers until you are ready to cook them.
3: Just before cooking, generously season the burgers on both sides with salt, turning them gently.
4: Heat the olive oil in a large skillet over medium-high heat. Add the burgers, spacing them 2 inches apart. Cook the burgers until the bottoms are browned, 3 to 5 minutes. Using a spatula, gently turn the burgers over and continue cooking them until done to taste, about 5 minutes more for medium. To test for doneness, insert an instant-read thermometer through the side of a burger. When the burger is cooked to medium the thermometer will register 165°F.
5: Transfer the burgers to a warm plate and let rest for 1 to 2 minutes.
6: Meanwhile, wipe out the skillet and use it to warm the tortillas over medium heat untilapliable, about 10 seconds per side. Use tongs to turn them. (If you cooked the burgers under the broiler or on the grill, warm the tortillas in either one for about 10 seconds per side.)
7: To serve, place a burger on one side of each tortilla. Spoon some salsa over each burger, if using, and top the burgers with jicama, avocado, and/or Rajas and sour cream, if desired. Fold the bare halves of the tortillas over the burgers and serve.
